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Lecture 4

BIOL 102 Lecture 4: Photosynthesis

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Clark University
BIOL - Biology
BIOL 102
David Hibbett

Photosynthesis II • Oxidation of H2O drives the Reduction of CO2 which drives the formation of carbohydrates • Light absorption results in photochemical change o Photosynthetic pigments are associated with proteins and found embedded in the thylakoid membranes ▪ Organized into structures known as light harvesting complexes, which contains chlorophyll a and other pigments (antenna system) and reaction centers ▪ In the reaction centers (contain chlorophyll a), light energy is converted to chemical energy ▪ Absorption of light excites chlorophyll (chlorophyll*  excited chlorophyll) ▪ Chlorophyll* + Acceptor  oxidized chlorophyll + reduced acceptor - ▪ Energy transfer in antennas by resonance (like the wave) • Reduction leads to ATP and NADPH formation o Electron are passed along the electron transport chain in the thylakoid membrane (series of reductions and oxidations) o Final e- acceptor is NADP+ + + - ▪ NADP + H + 2e  NADPH o ATP: produced chemiosomotically ▪ Proton gradient and ATP synthase ▪ Photophosphorylation ▪ Oxidative phosphorylation • Photosystems I and II o Photosystem II ▪ P 680– reaction center; site of photochemistry; maximum absorbance at 680nm • Responsible for the oxidation of water • Oxidizes water molecule and initiates electron transport • P 680+ Acceptor  P 680++ acceptor- + • P 680Very strong and unstable o Photosystem I ▪ P 700 + ▪ Chl* + acceptor  Chl + Acceptor • The acceptor is what reduces NADP  NADPH + • Chl the electrons come from electron transport chain • Oxygen is a byproduct of photosynthesis • Cyclic electron transport increases ATP production o Produce carbohydrates (Calvin Cycle – requires more ATP than NADPH) o Instead of linear flow of electrons, the electron transport will now have a cycling of electrons o ETC  P700 e-  ETC o Cyclic electron transport allows the cell to balance the ATP and NA
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